A gypsum board is known as an architectural interior finish material, which has a gypsum core covered with surface cover sheets. The surface cover sheet is exemplified as a sheet of paper for gypsum board liner, a glass fiber mat, a printed paper sheet or fiber mat, an organic resin coated paper sheet or fiber mat, a metal-laminated paper sheet or fiber mat. The gypsum boards are mass-produced by a gypsum board production apparatus, and are circulated in the domestic market of building materials. In general, the gypsum board production apparatus comprises a conveyance device for continuously conveying a sheet of paper for gypsum board liner (a lower sheet) which constitutes a first cover sheet; a scoring device which scores the edge zones of the sheet (lower sheet) on both sides; a mixer for preparation of gypsum slurry; a folding device folding the sheet for forming the edge portions; an upper sheet feeding device for overlaying the gypsum slurry with a sheet of paper for gypsum board liner (an upper sheet) which constitutes a second cover sheet; a forming device forming a layered formation of the upper sheet, the lower sheet and the gypsum slurry into a plate-like configuration; a severing device for severing a predetermined length of board from the plate-like belt formation; a dryer for forced drying of the severed boards containing excess water; a delivery device for cutting the board to be the product of a predetermined size and outputting the products, and so forth.
The forming device constituting the gypsum board production apparatus is known in the art, which causes the layered formation to pass through a forming gate defined by upper and lower plates, so that the upper and lower plates adjust or regulate the thickness of the layered formation passing therethrough (Japanese Patent Publication No. 2-18239 and Japanese Patent Laid-Open Publication No. 2000-71218).
In this kind of forming device, each of the upper and lower plates makes surface-to-surface contact with the layered formation under a considerably high pressure, in order to stabilize the configuration and thickness of the layered formation. Therefore, the upper and lower plates have to endure the heavy forming load acting thereon during the forming process, while maintaining the predetermined gate size. Thus, a thick metal plate with high rigidity is used as each of the upper and lower plates.
Publication 1: Japanese Patent Publication No. 2-18239
Publication 2: Japanese Patent Laid-Open Publication No. 2000-71218